1. Field of the Invention
This invention relates, in general, to flow cells for optical detectors, and more particularly to flow cells for chromatography systems, as well as methods for their manufacture and use.
2. Description of Related Art
Absorbance detectors are utilized in a wide variety of analysis applications including, but not limited to, high pressure liquid chromatography and ion chromatography. Generally, absorbance detectors have a flow cell through which sample flow is directed between two windows. Light is directed through the windows and sensed to determine the amount of light absorbed by the sample flowing between the windows. Typically, absorbance detectors have a linear range of about five orders of magnitude.
The typical flow cell has a pathlength of about 10 mm in length. However, samples coming from chromatography columns and other analytical equipment often are of sufficiently large concentration that the linear range of the optical detector is exceeded with a 10 mm pathlength cell. Thus, a cell with a shorter pathlength is required. The desired pathlength is in the 0.05-0.4 mm range in order to analyze concentrated samples, such as those exiting semi-prep chromatography columns, without exceeding the linear range of the optical detector. Such a small pathlength however, is typically on the order of, or shorter than, the diameter of the passageways that bring the sample flow into and out of conventional flow cells. As such, the configuration of conventional flow cells generally results with unswept volume, that is, volumes or spaces within the sample chamber of the flow cell in which sample flow may not reliably flow and instead may remain stagnant.
In addition, conventional flow cells typically utilize o-rings, gaskets, stepped lenses, and/or other sealing means in order to provide a liquid-tight seal between the windows and the cell body. Generally, such sealing means are applied some distance away from the pathlength in the sample chamber and results with a configuration having unswept volume.
What is needed is an improved flow cell which overcomes the above and other disadvantages of known flow cells.